Hybrid electromechanical coolant pump with base flow and peak flow

ABSTRACT

The invention relates to a coolant pump having an impeller which is arranged on a pump impeller shaft and having a drive device for the impeller, which drive device has a mechanical drive and an electric-motor drive. The impeller shaft is divided into a driving section and a driven section, and an openable and closable clutch is arranged between the driving section and the driven section.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation-in-part of U.S. patent application Ser. No. 12/937,746, filed on Feb. 6, 2011, and entitled “Coolant Pump.”

TECHNICAL FIELD

The present invention relates to coolant pumps which have both a mechanical mode of operation and an electric mode of operation.

BACKGROUND OF THE INVENTION

A coolant pump is known from DE 102 14 637 A1. To be able to realize different driving operation states of a vehicle with such a coolant pump, which has both an electric-motor drive and also a mechanical drive, a planetary drive is provided which can be driven by the electric motor and/or by the mechanical drive. However, such a design is complex with regard to its mechanical construction and is susceptible to operation inconsistencies.

It is therefore an object of the present invention to create a coolant pump with a simpler and more reliable design in relation to the prior art and whose operation is efficient and fail-safe.

SUMMARY OF THE INVENTION

In accordance with a preferred embodiment, the pump wheel shaft is divided into a driving section and a driven section which is separate from said driving section. A clutch is arranged between the driving section and the driven section and can be opened in order to separate said two sections and which can be closed in order to connect the two sections. With this embodiment, the pump wheel can be driven both by an electric-motor drive and also by a mechanical drive, in each case independently.

With the present invention, pumps are provided, such that the mechanical pump takes over the function of the electric pump in order to boost the pump power for operating conditions for which the electric pump would be inefficient or inadequate. It is also possible to obtain a fail-safe function for the electric pump, since it can be coupled to the mechanical pump if an interruption occurs in the electrical energy supply.

One of the features of the invention is that the operation of a heavy truck engine using a fully variable coolant pump showed that there is a need for two different flow volumes of coolant fluid. A smaller volume or amount of coolant flow (i.e. “base flow”) is needed to, for example, avoid hot spots in the engine. A higher volume or amount of coolant flow (i.e. “peak flow”) is needed to, for example, cool the vehicle in full load conditions.

In principle, the following implementations of the invention are possible:

(A) Although it is possible to operate both pump types in parallel, it is particularly preferably provided according to the invention that the electric pump and the mechanical pump be connected in series, with a regulated clutch performing the function of coupling in the mechanical pump, for example, on the basis of pressure measurements or monitoring of the electrical energy supply.

(B) In the case of a sequential arrangement of the mechanically operated pump and the electrically operated pump, it is preferable, for both pumps to use a single pump wheel.

(C) It is also possible according to the invention, as a result of a downsizing of the coolant pump, for said coolant pump to be adapted both for the utility vehicle field and also for the passenger vehicle field. In the case of the passenger vehicle field, the warm-up behaviour of the engine can be improved by precise adjustment of the basic coolant flow.

(D) In hybrid vehicles, the invention may also provide a coolant flow when the engine is stopped. The coolant flow is required for the functioning of the alternator/generator and for the battery. The coolant flow which is required may accordingly be provided by the combination according to the present invention of the electric pump and of the mechanically driven pump, without an auxiliary pump being required, as in the prior art.

The invention has numerous benefits and advantages:

(1) A fail-safe design of the entire system, since it is possible, when the electric-motor drive is deactivated, for the pump wheel to be actuated solely by the mechanical drive. The decoupling from the mechanical drive takes place by means of an actuation of the clutch. In the rest position of the clutch, the pump wheel shaft is driven by the mechanical drive. In this situation, the clutch could be held in a deactivated state by an electrical mechanism. In the event of an electrical failure, the clutch will automatically connect the mechanical drive to the pump wheel.

(2) Two operating principles for actuating a driving side, wherein the two driving sides can be decoupled entirely from the driven side, or the two driving sides can be decoupled only individually from the driven side.

(3) In-line concept for coupling/decoupling with electric-motor drive. The electric-motor drive, which is preferably designed as a brushless direct-current (“DC”) motor, is arranged on the driven side of the pump wheel shaft. The mechanical drive and also the electric-motor drive may, connected by the clutch, be arranged in alignment on the same axis of the coolant pump, and drive only a single pump wheel. This is a preferred embodiment.

(4) The concept of the coolant pump according to the invention is compatible with different coolant pump designs.

(5) If the coolant pump is for an internal combustion engine of a passenger vehicle, the coolant pump according to the invention can provide hydraulic energy when the internal combustion engine is at a standstill. Post-operation cooling can take place by the main pump wheel by operation of the electric motor.

(6) Sequential operating logic can be obtained with the coolant pump according to the invention, since the pump wheel can be driven either by the electric motor or by the mechanical drive.

(7) The bearings on the driving side and on the driven side can be arranged in alignment on the same axle.

(8) It is possible to recover electrical energy from the electric- motor drive (generator operation) when the pump wheel is being driven exclusively by the mechanical drive. From an energy aspect, this is particularly possible in the overrun mode of the internal combustion engine.

(9) The provision of sufficient cooling power for most operating states by decoupling the mechanical drive and operation by means of the electric motor.

(10) As a result of the cubic power characteristic curve of a coolant pump, the electric motor provides a basic volume flow. The maximum delivery power for maximum cooling power takes place by coupling the mechanical drive (without electric-motor pump).

BRIEF DESCRIPTION OF THE DRAWINGS

Further details, advantages and features of the present invention can be gathered from the following description of an exemplary embodiment on the basis of the drawing, in which:

FIG. 1 shows a sectioned illustration through an embodiment of a coolant pump according to the invention;

FIG. 2 shows a schematic construction of a cooling circuit of an internal combustion engine having the coolant pump according to the invention;

FIGS. 3 and 4 show two statistical distribution plots of the pump wheel rotational speed in relation to the engine speed for two transient driving cycles;

FIG. 5 depicts the power consumption for an embodiment of a coolant pump according to the invention;

FIGS. 6 and 7 show a coolant flow scenario and power consumption, respectfully, for an embodiment of a coolant pump according to the invention;

FIG. 8 is a cross-sectional view of an embodiment of a coolant pump according to the invention; and

FIG. 9 is a schematic illustration of a cooling circuit of an internal combustion engine utilizing an embodiment of the coolant pump according to the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows a sectioned illustration through a coolant pump 15 according to one embodiment of the invention. The coolant pump 15 has a pump wheel (also called an “impeller”) which is arranged on a pump wheel shaft (also called an “impeller shaft”). The pump wheel shaft is divided into a driving section 3 and a driven section 11. In the illustrated embodiment, the driving section 3 is formed as a flange-shape structure to which a mechanical drive 1, in the form of a belt pulley in this example, is rotationally fixedly connected. In the illustrated embodiment, the arrangement composed of a flange-shape structure 3 and a belt pulley 1 is mounted in a housing 7 by means of a bearing 6.

The mechanical drive 1 may be connected to an internal combustion engine of a motor vehicle, wherein in the illustrated embodiment, it is possible to use a belt drive. Only the belt pulley 1 is shown in order to simplify the illustration.

The driven section 11 of the pump wheel (impeller) shaft is mounted in the housing 7 by means of two bearings 6 and 10, and at its free end 16, supports the pump wheel 13. Here, the free end 16 of the driven section 11 is sealed off with respect to the housing 7 by means of a seal 12 which is arranged between the pump wheel 13 and the bearing 10.

As is also shown in FIG. 1, the driven section 11 and the driving section 3 of the pump wheel shaft can be connected by means of a clutch 4 which is arranged between the two sections 3 and 11. The clutch 4 may for example be embodied as an electromagnetic clutch with a coil 5.

An electric-motor drive is positioned in the driven section 11 of the pump wheel shaft, which electric-motor drive is arranged, with its rotor 9 and a stator 8 which surrounds said rotor 9, in axial alignment with the mechanical drive 3 on the driven section 11. Here, as shown in FIG. 1, the rotor 9 and the stator 8 are positioned in the housing 7.

An optional Hall effect device 14 can be arranged between the rotor 9 and the bearing 6.

With this design of the coolant pump 15 according to the invention, it is possible for the pump wheel 13 to be completely separated from the mechanical drive 1 by opening the clutch 4. Here, the electric-motor drive, which is preferably embodied as a brushless DC motor, is arranged on the side of the driven section 11 of the pump wheel shaft. This allows the electric motor drive to provide a regulable coolant flow in a predeterminable power range, which is independent of the rotational speed of the motor to which the coolant pump 15 is connected, when the driven section 11 is separated from the driving section 3 by the opened clutch 4.

For this purpose, the rotor 9 of the electric-motor drive is arranged directly on the driven section 11 of the pump wheel shaft, as can be seen from FIG. 1. The stator 8 is integrated, around the same axis of the housing 7, in the housing 7 around the rotor 9, as can likewise be seen from FIG. 1.

The electric-motor drive 8, 9 can be regulated by means of a commutated signal from an electronic regulating device (not illustrated in any more detail in FIG. 1). If the driven side 11 is separated from the driving side 3, the pump wheel 13 can be driven solely by the electric-motor drive. Here, it is provided that sufficient hydraulic output power is provided in order to provide the required coolant flow or all normal operating conditions of the engine which is connected to the coolant pump 15. To obtain a maximum available coolant flow, the driven section 11 can be connected to the driving section 3 of the pump wheel shaft by means of the clutch 4. In this case, the pump wheel 13 is driven solely by the mechanical drive 1 when the electric motor is deactivated.

FIG. 2 illustrates a schematic construction of a possible cooling circuit of an internal combustion engine 17 which uses the coolant pump 15 according to the invention. In this schematically highly simplified illustration, the pump which is driven by an electric motor is denoted by the reference symbol 20 and the mechanically driven pump is denoted by the reference symbol 21. The two pumps, which are arranged in series, may be connected via the clutch 4 to a belt drive 2 and via the belt pulley 1 to the engine 17 for the provision of the required mechanical drive energy. In the illustrated embodiment, the coolant circuit also has a thermostat 18 and a cooler member 19, such as a radiator, the interaction of which is shown by the arrows.

The coolant pump can be arranged in a sequential or parallel manner, wherein the electrical pump can be arranged in series or in parallel to the mechanical driven member. This includes serial/parallel operation in both mechanical and hydraulic manner (drive side or pump side).

FIGS. 3 and 4 show data of two transient driving cycles evaluated with a fully variable pump, with the curves and entries plotted therein. The graphs 50 and 60 show two occurrence plots, which show the flow requirement for two typical drive cycles. The two major occurrences of base flow 52 and 62, and peak flow 54 and 64 are depicted.

In the occurrence plot 50, the base flow 52 could be provided by the electrical pump drive at less than one kW power. The peak flow 54 could be provided by the mechanical pump drive at more than one kW power in the illustrated example.

FIG. 5 illustrates the power considerations of the two major modes for a variable coolant pump. The top graph 70 plots the power consumption of the coolant pump, showing the volume flow in liters per minute (1/min) versus the power (in kW). The area 72 is the preferred area for use of an electrical pump, and the area 74 is the preferred area for use of a mechanically driven pump. The borderline for determining the choice of pump and drive type is shown at 76. The borderline is one kW in the illustrated example.

The bottom graph 80 is the same as occurrence plot 60 in FIG. 4, and is the basis for the graph 70 and preferred areas 72 and 74, as well as borderline 76. On the basis of graph 80, the borderline for determining whether to use mechanical drive or electric drive in this example is at about 1500 rpm of the impeller.

The power considerations shown in FIGS. 3-5 depict the two major modes for a variable coolant pump. The base flow provided by the pump can be delivered by a pump driven by an electric motor, since the power consumption is below one kW. The power consumption above one kW is difficult to be achieved by an electric motor, mainly due to the lack of electrical power in common vehicles today. Here, a mechanically driven system is preferred. The mechanical drive provides a “boost” when more cooling is needed.

The discussed embodiment above also provides a “failsafe” coolant pump. If the electrical system or power in the vehicle were to fail or stop in some manner, the mechanical drive would take over and the coolant pump would be driven by the pulley and mechanical drive. This would allow the operator of the vehicle to continue to operate the vehicle until the electrical system failure could be repaired and reactivated.

In addition, the discussed embodiment can continue to deliver coolant through the system even when the engine is switched or turned off. The electrical drive powered by the battery of the vehicle can continue to operate the coolant pump and circulate the cooling fluid until the engine and other components are sufficiently cooled. Some vehicles today require use of an auxiliary pump to accomplish this.

Significant benefits and advantages of the invention include the following:

(i) Hydraulically parallel or sequential running electric and mechanical pumps with a controlled clutch on the mechanical member driven by the backpressure or electrical power of the electric pump system (the clutch is controlled by the electrical power supply of the electric pump system or by the back pressure of the coolant circuit);

(ii) Mechanically sequential running mechanical and electrical drive sharing one hydraulic member (i.e. impeller).

Beside these features, the inventive coolant pump can be downsized to the needs for the automotive market segment, where it could improve the warm-up behavior of the vehicle and engine by exactly applying the needed base flow with the speed of the electric motor.

In accordance with embodiments of the invention, the coolant pump drive can be completely decoupled from the FEAD drive side by the clutch, such as an electromagnetic clutch. The DC motor is integrated in the driven shaft axle to provide a controllable coolant flow in a defined performance range completely independent from the engine speed when the driven axle is decoupled from the drive shaft. For this, the rotor of the DC motor is directly mounted on the driven shaft, and is positioned between two bearings above and beneath the rotor. The stator is mounted in the coolant pump housing on the same axis.

The DC motor, which preferably is brushless, is controlled by a commutated signal from an electronic control device. If the driven side is decoupled from the drive side, the impeller can be driven by the DC motor. This will provide sufficient hydraulic power to meet the required coolant flow for most of the operating conditions of a vehicle. To achieve the maximum available coolant flow, the driven side is coupled with the drive side, for example, with an electromagnetic clutch. The impeller will then be driven by the FEAD.

As indicated, benefits and features of the embodiments of the invention include:

-   -   Failsafe function of the system, due to jointly supplied         voltage. The clutch will engage to drive the impeller by the         pulley, if the brushless DC motor is powered off     -   Inline concept of On/Off clutch with electronic motor. The DC         motor is mounted on the driven side. Both devices, clutch and DC         motor, are aligned on the same axis and are driving just one         impeller.     -   Hydraulic power can be provided at engine stop conditions.     -   Sequential operational logic where the impeller can be driven         simply by one device (electronic motor or by pulley).     -   Bearing of drive side and driven side are aligned on the same         axis.     -   Possible electric energy recovery from the brushless DC motor,         if the impeller is driven by the pulley.

FIGS. 6 and 7 are two additional graphs which illustrate the operations and benefits of embodiments of the present invention. FIG. 6 depicts the coolant flow verses engine speed, while FIG. 7 depicts the power consumption verses engine speed.

In FIG. 6, which is designated generally by the reference numeral 100, the line 102 depicts the engagement of the electromagnetic clutch. Line 104 depicts the amount of 20% of the coolant flow. This amount is controlled by the electric DC motor, particularly a brushless DC motor, and also is the maximum amount of flow that the electric motor can produce. Disengagement of the clutch is represented by the line 106.

With an electric DC motor, only about 5% of the total power is needed to provide about 20% of the coolant flow.

In FIG. 7, which is designated by the reference numeral 120, the line 122 depicts the power consumption when the electromagnetic clutch is engaged. Line 124 depicts the maximum power consumption by the DC motor, which is preferably brushless.

FIG. 8 depicts an embodiment 150 of a dual mode coolant pump in accordance with the invention. The pump includes a first body member 152 which is fixedly connected to a pulley member 154. The body member 152 is rotated at input speed by a belt member (not shown) attached to the vehicle engine. This provides the mechanical drive member for rotation of the coolant impeller 156.

Bearing member 158 allows the mechanical drive body member 152 to rotate freely when it is not needed to drive (rotate) the impeller member 156 and provide additional coolant flow to assist in cooling the engine.

The mechanical drive body member is situated inside a housing member 160. When the coolant pump 150 is in use, the housing member 160 is attached to the vehicle engine or another component or housing which in turn is attached to the engine and in fluid communication with the engine coolant system.

Impeller shaft member 162 is positioned centrally inside the housing 160. The shaft member 162 is fixedly secured at one end 162-A to the impeller member 156. The other end of the shaft member 162-B is secured to an openable and closeable clutch mechanism 170. The clutch mechanism 170 is preferably an electromagnetic clutch mechanism and is operated by electric coil 180.

The impeller shaft member 162 is rotatably positioned inside the housing 160 by a pair of bearing members 172 and 174. An electric motor 190, which preferably is a brushless DC motor, is positioned in the housing and situated between the two bearing members 172, 174. The motor 190 includes a stator member 192 and a rotor member 194. The rotor member 194 is fixedly secured to the impeller shaft member 162 and rotates with it.

A sealing member 196 is used to isolate the coolant fluid (in which the impeller 156 is positioned) from the components of the coolant pump 150. In addition, an optional Hall Effect Device (HED) 198 is positioned in the housing adjacent the rotor member in order to monitor the speed of rotation of the impeller shaft and provide data to a computer control system, such as, for example, an electronic control unit (ECU). The data generated and supplied by the HED as well as other possible data supplied by other sensors, generally controls the operation of the coolant pump.

The cooling pump 150 is a dual mode coolant pump for operating and controlling the operation of the rotation of the impeller and thus the flow of coolant in the engine and/or vehicle cooling system. Under normal conditions, the impeller is operated by the electric motor 190. Under these conditions, the electromagnetic clutch mechanism 170 is held in an open condition by power from the coil member 180. When more cooling is needed, or in a failsafe situation where electric power is lost to the coolant pump, the clutch mechanism 170 closes and the shaft member 162 is rotated by the mechanical drive member 152.

As indicated in the description of FIG. 8, the first body member 152 comprises the mechanical drive mechanism for the coolant pump, while the electric motor 190 comprises the driven drive mechanism for the coolant pump.

FIG. 9 schematically depicts a cooling system 200 for a vehicle engine, as well as a control system 230 for the cooling system. The cooling system includes a vehicle engine 202, a thermostat 204, a heat exchanger 206, such a as a radiator, and a dual mode coolant pump 208. The coolant pump 208 includes a pulley member 210, a mechanical drive mechanism 212, a clutch mechanism 214, and a DC electric motor 216.

The coolant pump 208 could be, for example, the coolant pump 150 discussed above and shown in FIG. 8.

The pulley member 210 is driven by a belt 220 from a pulley member 222 attached to and rotated by the vehicle engine 202. Engine coolant flows from the engine 202 through the radiator 206 and then through the coolant pump 208 before being directed back to the engine.

The control system 230 includes an electronic control unit (ECU) 232 which controls the operation of the coolant pump 208. The ECU receives data from various sensors, such as one or more temperature sensors 234, which assist in directing the operation of the cooling system. Also, control logic 240 in the coolant pump 208 can be supplied to operate the various coolant pump components and mechanisms. The ECU 232 can also be in communication and receive data from one or more other ECUs in the engine and vehicle.

With the present invention, the coolant pump drive can be completely decoupled from the FEAD drive side by, for example, an electromagnetic clutch. A brushless DC motor integrated with the driven shaft member to provide a controllable coolant flow in a defined performance range independent from the engine speed. For this, the rotor of the brushless DC motor is directly mounted on the driven shaft member with roller bearings positioned above and beneath the rotor. The stator is mounted in the coolant pump housing on the same axis.

The brushless DC motor is controlled by a commutated signal from an electronic control unit. If the driven side is decoupled from the drive side, the impeller is driven by the brushless DC motor. It is designed to provide sufficient hydraulic power to meet the required coolant flow for the most of the operating conditions of a vehicle. To achieve the maximum available coolant flow, the driven side is coupled with the drive side, by, for example, an electromagnetic clutch. The impeller will then be driven by the FEAD.

The present invention provides at least the following:

-   -   A failsafe system, due to jointly supply voltage. The clutch         will engage to drive the impeller by the pulley, if the         brushless DC motor will be powered off     -   Inline Concept of On/Off clutch with electronic motor. The         brushless DC motor is mounted on the driven side. Both devices,         clutch and brushless DC motor, are aligned on the same axis and         are both positioned operably to drive the same impeller.     -   Hydraulic power can be provided at engine stop condition.     -   Sequential operation logic in which the impeller can be driven         just by one device (electronic motor or by pulley).     -   Bearings on the drive side and the driven side are aligned on         the same axis.

Electric energy recovery from the brushless DC motor when the impeller is driven by the pulley.

While preferred embodiments of the present invention have been shown and described herein, numerous variations and alternative embodiments will occur to those skilled in the art. Accordingly, it is intended that the invention is not limited to the preferred embodiments described herein but instead limited to the terms of the appended claims. 

What is claimed is:
 1. A coolant pump for rotating an impeller shaft comprising: a housing member having a first end and a second end; an impeller shaft member positioned in said housing member; an impeller member positioned externally to said first end of said housing member and connected to one end of the impeller shaft member and rotatable therewith; a pair of first bearing members positioned in said housing member and positioned on said impeller shaft to allow rotation of said impeller shaft in relation to said housing member; a pulley member positioned adjacent said second end of said housing member; a second bearing member positioned in said housing member to allow rotation of said pulley member relative to said housing member; a mechanical drive body member positioned in said housing member and having a first end and a second end, said first end being fixedly attached to said pulley member; wherein said mechanical drive body member is rotatable with said pulley member; an electric motor having a rotor member and a stator member, said electronic member positioned in said housing member; said rotor member being fixedly connected to said impeller shaft member and rotatable therewith; and an electromechanical clutch mechanism positioned in said housing between said second end of said mechanical drive body member and said electronic motor; wherein activation of said electromechanical clutch mechanism prevents said mechanical drive body member from rotating said impeller shaft member; and wherein deactivation of said electromechanical clutch mechanism couples said mechanical drive body member to said impeller shaft member, thereby rotating said impeller shaft member at the rotation speed of said pulley member.
 2. The coolant pump as described in claim 1 wherein said electric motor is a brushless DC motor.
 3. The coolant pump as described in claim 1 wherein said electromechanical clutch mechanism is deactivated when the impeller shaft member is rotating at a speed greater than a predetermined speed threshhold.
 4. The coolant pump as described in claim 3 wherein said speed threshold is about 150 rpm.
 5. The coolant pump as described in claim 1 wherein said rotor member is positioned between said pair of first bearing members.
 6. The coolant pump as described in claim 1 wherein said electromechanical clutch mechanism is deactivated when the power to the electric motor is greater than a predetermined power threshold.
 7. The coolant pump as described in claim 6 wherein said predetermined power threshold is about 1 kW.
 8. The coolant pump as described in claim 1 wherein said electromechanical clutch mechanism comprises a friction clutch mechanism, an armature member and a solenoid member.
 9. The coolant pump as described in claim 1 further comprising a Hall effects sensor.
 10. A coolant pump comprising: a pump wheel which is arranged on a pump wheel shaft; a drive device for said pump wheel, said drive device having a mechanical drive and an electric-motor drive; said pump wheel shaft being divided into a driving section and a driven section; and an openable and closable clutch positioned between said driving section and said driven section; wherein when said driven section is separated from said mechanical drive and the driving section, said pump wheel can be driven solely by said electric-motor drive.
 11. The coolant pump as set forth in claim 1, wherein said mechanical drive comprises a belt-pulley drive.
 12. The coolant pump as set forth in claim 1, wherein said driven section comprises said electric-motor drive.
 13. The coolant pump as set forth in claim 1, wherein said electric-motor drive comprises a brushless direct-current motor.
 14. The coolant pump as set forth in claim 1 wherein said electric-motor drive has a rotor member which is positioned in said driven section, and a stator member which is positioned around said rotor member wherein said rotor member and said stator member are positioned concentrically with respect to one another and in a housing.
 15. The coolant pump as set forth in claim 1 wherein said clutch comprises an electromagnetic clutch.
 16. The coolant pump as set forth in claim 1 wherein said electric-motor drive is regulated by an electronic regulating device.
 17. The coolant pump as set forth in claim 1 further comprising bearing for mounting said pump wheel shaft, said bearings having rotating inner rings.
 18. The coolant pump as set forth in claim 1 wherein said electric-motor pump, which is formed by said electric-motor drive and by said pump wheel, provides a basic coolant flow, and wherein said mechanical pump is formed by said mechanical drive and said pump wheel and can be coupled by said clutch in order to deliver a maximum cooling power.
 19. The coolant pump as set forth in claim 18 wherein said electric-motor pump and said mechanical pump are arranged in series.
 20. The coolant pump as set forth in claim 1 wherein said mechanical drive and/or said electric-motor drive, can be decoupled from said driven section.
 21. The coolant pump as set forth in claim 1 wherein said mechanical drive is coupled to said driven section when the electric-motor drive is not supplied with current.
 22. The coolant pump as set forth in claim 1 wherein when said driven section (11) is coupled to said mechanical drive and said driving section by said clutch, said pump wheel is driven solely by the mechanical drive and said electric-motor drive is deactivated. 